1. Field of the Invention
The present invention relates to a harbor crane for normal and heavy load operation having an undercarriage, a superstructure mounted on the undercarriage, a tower fastened on the superstructure, and a jib arranged on the tower for pivoting about a horizontal axis, the jib in normal operation being held pivotably on the superstructure by a luffing cylinder coupled to the jib and to the tower, wherein the load is liftable by a hoisting cable guided to the jib head and having a snatch block suspended on it.
2. Description of the Related Art
Mobile harbor cranes are frequently also designed for use in heavy load operations. For this purpose, the structural measures necessary for lifting these heavy loads must be provided. The additional structural measures may comprise, for example, relatively strong hoisting mechanisms which can be reversed, relatively strong cables and classification matched to the heavy load to be lifted. Depending on the size of the equipment, normal mobile harbor cranes are able to handle heavy loads of up to 120 t. The ratio of normal load to heavy load is approximately 1:2.
If a load needs to be handled that is greater than the capacity of the crane, two mobile harbor cranes are used in a tandem operation. However, tandem operation requires careful planning and preparation and time-consuming implementation because the coordination of the two mobile harbor cranes is not without risk. Another option for the harbor operator is to use a floating or truck-mounted crane having an appropriately high load-bearing capacity. However, this considerably increases the cost of handling the load and depends on the availability of cranes which can be hired.
The object of the present invention is to refit a conventional mobile harbor crane with accessory equipment such that the crane is usable in both a normal mode of operation and in heavy load mode of operation with justifiable structural measures and with short setting-up times.
The object the present invention is met by a harbor crane having conventional components including a superstructure, a tower arranged on the superstructure, a jib pivotably arranged on the tower, a luffing cylinder for luffing the jib, and a hoisting mechanism, and hoisting cable guided from the hoisting mechanism to the head of the jib for lifting a load. According to the invention, additional components are fitted on the harbor crane for a heavy load operating mode including a heavy load lifting winch fixed to the superstructure of the harbor crane, preferably below the jib. A heavy load lifting cable is guided from the heavy load lifting winch over a deflecting roller fastened to the jib and guided to the roller assembly of a heavy load snatch block arranged releasably on the jib head. The normal load lifting mechanism of the harbor crane is used in heavy load operating mode as a luffing mechanism for the jib, for which purpose the normal load hoisting cables are detached from the normal load snatch block and fixed to the jib head. During the heavy load operating mode, the unloaded luffing cylinder serves as a fall-back support for the jib. Furthermore, the righting moment of the mobile harbor crane is increased during heavy load operating mode as compared with normal load operating mode.
The components of the harbor crane which are subjected to increased stress because of the additional heavy load equipment such as, for example, the jib, tower, rotary connection and crane support, and their connection constructions are reinforced as required, i.e. only when there is a corresponding increase in carrying load.
A harbor crane having the above-described equipment for heavy-load operation avoids the problems of the prior art. The function and basic structure of a conventional mobile harbor crane are not affected by the additional equipment. The luffing mechanism used during heavy load operation is the hoisting mechanism of the mobile harbor crane so that the piston-cylinder unit of the luffing cylinder is unloaded during heavy load operation. At the same time, the luffing cylinder provided for normal operation serves in heavy load operation as a fall-back support for the jib.
In addition, for heavy load operation a further hoisting mechanism comprising a heavy load lifting winch is provided for lifting the heavy loads. To lift heavy loads securely, the righting moment which is configured for normal load operation of the mobile harbor crane should be increased.
In a further embodiment of the present invention, the righting moment of the mobile harbor crane in heavy load operation may be increased by extending a counter jib which is coupled to the tower on the side opposite the jib away from the tower in a vertical jib pivoting plane. The pivoting of the counter jib may be effected by a pivoting cylinder which also acts as a fall-back support Furthermore, the inclination of the counter jib may be changed via a bracing means fixed in a length-changeable manner at one end to the jib head and at the other end in the foot region of the tower. A head end of the counter jib is arranged for accommodating a supporting device for an additional heavy load counterweight which can be suspended in the vicinity of the ground and whose range of swing can be set by changing the inclination of the counter jib.
In this embodiment of the present invention, the righting moment of the mobile harbor crane is increased. The counter jib, which remains on the apparatus during normal load operation, is extended rearward by a pivoting cylinder and guides and supports the additional heavy load counterweight which is suspended at the head end of the counter jib at the required operative radius. By adjusting the inclination of the counter jib, the range of swing and therefore the counterweight moment may be varied without any problem within a tolerance range.
In a further embodiment of the present invention, the bracing means for changing the inclination of the counter jib comprises bracing rods which are fixed to the jib head. The free ends of the bracing rods may be coupled to deflecting rollers for a respective cable which in heavy load operation is fastened to the counter jib head and is guided via a deflecting roller arranged on the counter jib head to a setting mechanism (winch) arranged on the tower. This solution enables the inclination of the counter jib to be adjusted via the setting mechanism, generally a winch, by the cable being hauled in or made slack.
It is particularly favorable if during normal operation of the harbor crane, the bracing rods are fixed to the jib head are placed on the jib and attached there, and the deflecting rollers detached from their free ends are in each case fastened, with reeved cable, to the head of the tower, each cable being set in the manner prescribed by the counter jib in its upright inoperative position locked by the pivoting cylinder, and the supporting device for the suspended heavy load counterweight being attached to the superstructure. That is, all of the essential parts of the accessory equipment for increasing the carrying load of the mobile harbor crane remain on the vehicle and therefore refitting from normal operation to heavy load operation occurs very rapidly. In particular, the cables largely remained reeved, rendering complicated threading work unnecessary. Further, the heavy load snatch block is temporarily stored in the vicinity of the heavy load hoisting mechanism on the superstructure of the harbor crane during the normal operation of the harbor crane with the heavy load hoisting cable reeved. In practice, the jib is lowered and the heavy load snatch block may be picked up by a forklift truck and with the cable reeved transported to a holding device which is provided on the superstructure of the mobile harbor crane. While the heavy load snatch block is being moved, the hoisting cable is wound up by the heavy load hoisting mechanism without leaving the roller assembly. The hoisting cable is removed only from the guide roller additionally provided on the jib, otherwise all of the cables remain reeved when changing from the heavy load operating mode to the normal operating mode.
To further reduce the setting-up times of the mobile harbor crane, the heavy load counterweight may be designed so that it can be moved, for example on a transport truck which can very easily be transported to the location of use where the supporting device of the counter jib picks up the heavy load counterweight.
The accessory equipment according to the present invention comprises a particularly cost-effective supplement to an existing mobile harbor crane. The re-equipping of a conventional crane to form the heavy load crane is possible within the shortest time and with the lowest outlay because to a large extent all of the parts required for this purpose are provided or are mounted on the mobile harbor crane. The operator of the mobile harbor crane does not have to hire firms offering truck-mounted or deck cranes to move heavy loads. Instead, the operator can himself adapt his equipment within the shortest time to the heavy load requirements.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.